Numerical control apparatus

ABSTRACT

A numerical control apparatus includes a command argument determination unit which determines whether a vector is included in an argument of a circular arc interpolation command which is included in command data and a circular arc shape forming unit which forms a circular arc shape based on a machining program, and a start point, an end point, and the vector, which are specified by the argument of the circular arc interpolation command, when the command argument determination unit determines that the vector is included in the argument of the circular arc interpolation command.

RELATED APPLICATION DATA

This application claims priority under 35 U.S.C. §119 and/or §365 toJapanese Application No. 2014-216553 filed Oct. 23, 2014, the entirecontents is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a numerical control apparatus and inparticular, the present invention relates to a numerical controlapparatus which is capable of specifying shapes of a circular arc and acurved surface which have small curvatures.

2. Description of the Related Art

Conventionally, when a circular arc shape is specified by a machiningprogram, a method for specifying a circular arc shape based on a startpoint, an end point, and a radius from the center is commonly known.Further, a specifying method in which coordinates of a start point, anend point, and a point on a circular arc are specified is also widelyknown.

For example, FIG. 10A illustrates an example in which a circular arcshape is specified by a start point, an end point, and a radius from thecenter. In a circular arc interpolation command “G02 Xp Yp R”, Xpdenotes an end point coordinate on a first axis of a plane, Yp denotesan end point coordinate on a second axis, and R denotes a distance fromthe center. Alternatively, a circular arc shape can be specified asillustrated in FIG. 10B. In a circular arc interpolation command “G02 XpYp I J”, Xp denotes an end point coordinate on a first axis of a plane,Yp denotes an end point coordinate on a second axis, I denotes adistance from a start point of the Xp axis to the center of a circulararc, and J denotes a distance from a start point of the Yp axis to thecenter of the circular arc.

As another prior art technique for specifying a circular arc shape, amethod is disclosed in which one point on a perpendicular bisector,which is orthogonal to a specific plane, of a line segment, which isobtained by connecting a start point and an end point, on the plane isselected so as to form a trajectory on a circular arc for avoidance ofan interfering object (for example, Japanese Patent ApplicationLaid-Open No. 10-161728).

FIG. 10C illustrates an example in which a circular arc shape isspecified by specifying a start point, an end point, and a middle pointon a circular arc. In this specifying method, a circular arc shape in athree-dimensional space can be specified. In a circular arcinterpolation command illustrated in FIG. 10C, Xxn denotes a coordinateon a first axis in a three-dimensional space, Yyn denotes a coordinateon a second axis, and Zzn denotes a coordinate on a third axis.

However, in the method for specifying a circular arc shape by a startpoint, an end point, and a radius from the center, the number of commanddigits exceeds a specification of a numerical control apparatus andtherefore, a circular arc shape cannot be specified in a case where acurvature is exceedingly small such as several μm of a width between thestart point and the end point and 5 km of a radius from the center asillustrated in FIG. 11, for example. In such a case, a curved surfaceneeds to be specified in a manner to be divided into a minute straightline segments. Therefore, there have been such problems that a CAD/CAMsystem is separately required and a size of a program is increased.

Further, in the technique described on Japanese Patent ApplicationLaid-Open No. 10-161728, a plane on which a circular arc shape is formedis previously determined, so that it is impossible to form an arbitrarycircular arc shape in a three-dimensional space. Further, a point whichis specified other than a start point and an end point needs to be seton a perpendicular bisector of a line segment which is obtained byconnecting the start point and the end point. Therefore, there is suchproblem that a load is imposed on an operator who creates a program.Furthermore, in the method described on Japanese Patent ApplicationLaid-Open No. 10-161728, it is impossible to deal with machining of aspherical surface shape and the like.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a numerical controlapparatus which is capable of easily specifying a circular arc shape inspecification of a circular arc shape by a machining program.

According to the present invention, a numerical control apparatus whichenables specification of a movement trajectory of a circular arc shapeby a circular arc interpolation command which is included in a machiningprogram includes a program analysis unit which analyzes the machiningprogram so as to acquire command data, a command argument determinationunit which determines whether a vector is included in an argument of thecircular arc interpolation command which is included in the commanddata, a circular arc shape forming unit which forms a circular arc shapebased on the machining program, and a start point, an end point, and thevector, which are specified by the argument of the circular arcinterpolation command, when the command argument determination unitdetermines that the vector is included in the argument of the circulararc interpolation command, and a tool trajectory forming unit whichforms a tool trajectory based on the circular arc shape.

The command argument determination unit may determine whether thecircular arc interpolation command is a machining command of a curvedsurface shape, the numerical control apparatus may further include aspherical surface shape forming unit which forms a spherical surfaceshape including a circular arc shape which is formed by the circular arcshape forming unit when the command argument determination unitdetermines that the circular arc interpolation command is a machiningcommand of a curved surface shape, and the tool trajectory forming unitforms a tool trajectory based on the spherical surface shape.

The spherical surface shape may be a hemispherical surface shapeincluding the circular arc shape, or a semi-circular column shape.

In the present invention, the above-mentioned configuration is provided,whereby a direction and a length of a vector with respect to a point ona circular arc shape which is specified based on a start point and anend point of a circular arc and a point on a straight line obtained byconnecting the start point and the end point is specified inspecification of a circular arc shape by a machining program.Accordingly, machining in which a circular arc shape is specified isenabled. Therefore, even when the number of command digits of anumerical control apparatus is limited, a circular arc shape and acurved surface shape which have exceedingly small curvatures can beefficiently specified, the size of a storage memory in which themachining program is stored can be reduced, and a workload, which isrequired for creation and revision of a machining shape, of a machiningprogrammer can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described and other objects and features of the presentinvention will be apparent from description of the following embodimentin reference to the accompanied drawings. Among these drawings,

FIGS. 1A and 1B illustrate a method for specifying a circular arc shapeaccording to an embodiment of the present invention;

FIGS. 2A and 2B illustrate a method for specifying a circular arcinterpolation command according to the embodiment of the presentinvention;

FIG. 3 illustrates a tool trajectory which is calculated in accordancewith a program example of the circular arc interpolation commandaccording to the embodiment of the present invention;

FIGS. 4A and 4B illustrate a method for specifying a curved surfaceshape command of a semi-curved surface shape according to the embodimentof the present invention;

FIG. 5 illustrates a tool trajectory which is calculated in accordancewith a program example of the curved surface shape command of asemi-curved surface shape according to the embodiment of the presentinvention;

FIGS. 6A and 6B illustrate a method for specifying a curved surfaceshape command of a semi-circular column shape according to theembodiment of the present invention;

FIG. 7 illustrates a tool trajectory which is calculated in accordancewith a program example of the curved surface shape command of thesemi-circular column shape according to the embodiment of the presentinvention;

FIG. 8 is a major portion block diagram of a numerical control apparatusaccording to the embodiment of the present invention;

FIG. 9 is a schematic flowchart of processing which is executed on thenumerical control apparatus according to the embodiment of the presentinvention;

FIGS. 10A, 10B, and 10C illustrate a method for specifying a circulararc shape of prior art technique; and

FIG. 11 illustrates a problem of the method for specifying a circulararc shape of prior art technique.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method for specifying a circular arc shape in the present invention isfirst described.

In the present invention, a circular arc shape is specified byspecifying a direction and a length of a vector from a point on astraight line, which is obtained by connecting a start point and an endpoint, to a point on the circular arc shape and a distance from thestart point of a circular arc to an origin of the vector, as illustratedin FIG. 1A.

In order to realize such specifying method, a specifying method of acircular arc interpolation command illustrated in FIGS. 2A and 2B isintroduced.

In FIG. 2A, Xxn denotes an end point coordinate on an X axis direction,Yyn denotes an end point coordinate on a Y axis direction, Zzn denotesan end point coordinate on a Z axis direction, Iin, Jjn, and Kkn denotea direction of a vector from a point on a straight line, which isobtained by connecting a start point and an end point, Lln denotes alength of the vector, and Mmn denotes a distance from the start point ofa circular arc to an origin of the vector.

As illustrated in FIGS. 2A and 2B, circular arc interpolation commandsG02 and G03 enables arguments Iin, Jjn, and Kkn for specifying thedirection of a vector with respect to a point on a circular arc shape,an argument Lln for specifying the length of the vector, and an argumentMmn for specifying the distance from the start point of a circular arcto the origin of the vector to be specified.

In the present specifying method, a start point of a circular arc shapeis defined by a positioning command G00 and the like and then, an endpoint of the circular arc shape, a direction and a length of a vectorwith respect to a point on the circular arc shape, and a distance fromthe start point of a circular arc to an origin of the vector arespecified by the circular arc interpolation command G02, for example, soas to provide a moving command of the circular arc shape. Here, in acase where similar circular arc shapes are continuously specified, thespecified direction and length of the vector and the distance from thestart point of the circular arc to the origin of the vector are takenover to a following block.

Accordingly, in a case of consecutive circular arc shapes which haveidentical specified directions of a vector, identical lengths of thevector, and identical distances from a start point of a circular arc toan origin of the vector, the shapes can be specified only by specifyingan end point of the circular arc. Thus, a size of a storage memory of aprogram can be reduced compared to methods of prior art. Further, anorigin of a vector is usually a middle point on a straight line which isobtained by connecting a start point and an end point. In this case, adistance from the start point of a circular arc to the origin of thevector can be omitted. FIG. 3 illustrates an example of a tooltrajectory which is drawn by a descriptive example of the circular arcinterpolation command illustrated in FIG. 2B.

A procedure for forming a circular arc shape based on a command, whichis specified by a circular arc interpolation command, of a machiningprogram according to the present invention is described below. In a casewhere a start point coordinate of a circular arc shape is (Xs,Ys,Zs), anend point coordinate of a circular arc shape is (Xe,Ye,Ze), and adistance from the start point coordinate of a circular arc to an originof a vector is Mm, a coordinate (Xvs,Yvs,Zvs) of the origin of thevector is obtained by using formula (1) below. The start pointcoordinate, the end point coordinate, and the distance are specified bya command of a machining program. In formula (1), Q denotes a distancefrom a start point of the circular arc shape to an end point of thecircular arc shape.

$\begin{matrix}{\left( {{Xvs},{Yvs},{Zvs}} \right) = {\left( {\frac{{\left( {Q - {Mm}} \right)*{Xs}} + {{Mm}*{Xe}}}{Q},\frac{{\left( {Q - {Mm}} \right)*{Ys}} + {{Mm}*{Ye}}}{Q},\frac{{\left( {Q - {Mm}} \right)*{Zs}} + {{Mm}*{Ze}}}{Q}} \right).}} & (1)\end{matrix}$

Then, a point (Xve,Yve,Zve) on the circular arc is obtained by usingformula (2) below based on the coordinate (Xvs,Yvs,Zvs) of the origin ofthe vector, a direction (I,J,K) of the vector, and a length L of thevector.

$\begin{matrix}{\left( {{Xve},{Yve},{Zve}} \right) = {\left( {{{Xvs} + \frac{{Ll}*{Ii}^{2}}{\sqrt{{Ii}^{2} + {Jj}^{2} + {Kk}^{2}}}},{{Yvs} + \frac{{Ll}*{Jj}^{2}}{\sqrt{{Ii}^{2} + {Jj}^{2} + {Kk}^{2}}}},{{Zvs}\frac{{Ll}*{Kk}^{2}}{\sqrt{{Ii}^{2} + {Jj}^{2} + {Kk}^{2}}}}} \right).}} & (2)\end{matrix}$

Finally, a circular arc shape, which passes through three points whichare the start point coordinate (Xs,Ys,Zs) of the circular arc shape, theend point coordinate (Xe,Ye,Ze), and the coordinate (Xve,Yve,Zve) of thepoint on the circular arc, is obtained.

Further, in the present invention, in a case where a curved surface inthe form of a spherical surface illustrated in FIG. 1B is machined, amachining shape can be specified by a method same as the above-describedcircular arc shape specifying method when a length of a line segment,which is obtained by connecting a start point and an end point, is setto a diameter of a circular shape of a base. Here, a direction of avector is a normal line direction with respect to a base circle in thiscase.

In order to realize such specifying method, a curved surface shape inthe form of a hemisphere surface is enabled to be specified by a curvedsurface shape command illustrated in FIG. 4A. Here, Xxn denotes an endpoint coordinate on the X axis direction, Yyn denotes an end pointcoordinate on the Y axis direction, Zzn denotes an end point coordinateon the Z axis direction, Iin, Jjn, and Kkn denote a direction of avector from a point on a straight line, which is obtained by connectinga start point and an end point, Lln denotes a length of the vector, andMmn denotes a distance from the start point of a circular arc to anorigin of the vector.

As illustrated in FIGS. 4A and 4B, arguments which can be specified havea similar meaning to that of the above-described arguments of thecircular arc interpolation command for specifying a circular arc shape,in a curved surface shape command G02.7. A machining region, which isspecified by this curved surface shape command, of a hemispherical shapeis within a range of a circle a diameter of which is a line segmentobtained by connecting the start point and the end point, and a vector(Iin,Jjn,Kkn) is a normal line vector of the circle.

A numerical control apparatus to which the present invention isintroduced automatically forms a specified tool trajectory on aspherical surface when a machining region of a hemispherical shape iscalculated based on a curved surface shape command specified by amachining program. The numerical control apparatus is capable of forminga continuous tool trajectory toward a single direction and is alsocapable of machining on a contour line in a circumference direction asillustrated in FIG. 5. Intervals of respective tool trajectories may beset in reference to an offset amount in a tool radius direction.

An example of a procedure for forming a tool trajectory of a semi-curvedsurface based on a curved surface shape command which is specified by amachining program is described below. A coordinate (Xve,Yve,Zve) of apoint on a spherical surface is first calculated by using formula (1)and formula (2) based on information, which is specified by the curvedsurface shape command, of a circular arc shape.

Then, a plane which includes a straight line, which is obtained byconnecting a start point and an end point of a circular arc, and isorthogonal to a direction of a vector is obtained.

Further, a circle which exists on the plane, a center of which is amidpoint of the straight line obtained by connecting the start point andthe end point, and a diameter of which is a length of the straight lineis obtained.

Then, a perpendicular bisector of the straight line, which is obtainedby connecting the start point and the end point of the circular arc, onthe plane is obtained and an intersection point of the obtainedperpendicular bisector and the above-mentioned circle is denoted as apoint P. Four points which are the start point of the circular arc, theend point of the circular arc, the point (Xve,Yve,Zve), and the point Pare substituted into formula (3) below so as to obtain coefficients A,B, and C. Thus, an equation of a sphere which passes through the fourpoints is obtained.

x ² +y ² +z ² +Ax+By+Cz+D=0   (3)

A central coordinate and a radius of a spherical surface shape and aheight of a machining region are obtained from formula (3), so that atool trajectory can be obtained by prior art technique.

As a further application of the present embodiment, a semicircularcolumn shape can be easily specified by a method same as the circulararc shape specifying method described above.

In order to realize specification of a semicircular column shape, acurved surface shape of the semicircular column shape is enabled to bespecified by a curved surface shape command illustrated in FIG. 6A.Here, Xxn denotes an end point coordinate on the X axis direction, Yyndenotes an end point coordinate on the Y axis direction, Zzn denotes anend point coordinate on the Z axis direction, Iin, Jjn, and Kkn denote adirection of a vector from a point on a straight line, which is obtainedby connecting a start point and an end point, Lln denotes a length ofthe vector, Mmn denotes a distance from the start point of a circulararc to an origin of the vector, and Hhn denotes a length of a linesegment toward a direction orthogonal to the vector centering on theorigin of the vector.

As illustrated in FIG. 6A, in a curved surface shape command G02.8,arguments which can be specified are an argument Hhn for specifying alength of a line segment which extends toward an orthogonal direction ofthe vector and a center of which is the origin of a vector, in additionto a vector equivalent to an argument of a circular arc interpolationcommand for specifying a circular arc shape described above. A machiningregion, which is specified by this curved surface shape command, of thesemicircular column shape is set to be a range of a shape of a base of arectangle, central lines of which are a line segment obtained byconnecting a start point and an end point and a straight line which isorthogonal to the line segment and has the length Hhn. Further, a vector(Iin,Jjn,Kkl) is a normal line vector of a rectangular shape which is abase of the semicircular column shape.

The numerical control apparatus according to the present embodimentautomatically forms a specified tool trajectory on a semicircular columnwhen a machining region of a semicircular column shape is calculatedbased on a curved surface shape command specified by a machiningprogram. The numerical control apparatus is capable of forming acontinuous tool trajectory toward a single direction and is also capableof machining by other tool trajectories, as illustrated in FIG. 7.Intervals of respective tool trajectories may be set in reference to anoffset amount in a tool radius direction.

An example of a procedure for forming a tool trajectory of asemicircular column surface based on a curved surface shape commandwhich is specified by a machining program is described below. Twostraight lines A and B which are on a plane orthogonal to a specifiednormal line vector, is orthogonal to a straight line obtained byconnecting a start point and an end point, and pass through the startpoint and the end point of a circular arc shape are first obtained.

Then, a circular arc shape is obtained by the above-describedcalculation method based on information of the specified circular arcshape. As regarding a circular arc shape adjacent to the circular arcshape which is the central circular arc shape, points are obtained byshifting from the start point and the end point of the circular arc byan offset amount of a radius of a tool, which is used in machining, onthe above-described straight lines A and B and the obtained points areset to be a start point and an end point of a new circular arc shape.The circular arc shape can be obtained by a similar method to theabove-described calculation method of a circular arc shape.

A circular arc shape group which becomes a tool trajectory can becalculated by repeating the shift up to the range of the length Hh.

FIG. 8 is a major portion block diagram illustrating a numerical controlapparatus according to the embodiment to which the above-describedspecifying method of a circular arc shape according to the presentinvention is introduced. A numerical control apparatus 100 is providedwith a program analysis unit 110, a command argument determination unit120, a circular arc shape forming unit 130, a curved surface shapeforming unit 140, a tool trajectory forming unit 150, and a distributionprocessing execution unit 160.

The program analysis unit 110 reads a machining program 200 from amemory (not illustrated in the drawing) and analyzes the machiningprogram 200 so as to output command data.

The command argument determination unit 120 determines whether acircular arc interpolation command or a curved surface interpolationcommand is included in the command data outputted by the programanalysis unit 110. When the circular arc interpolation command isincluded, the command argument determination unit 120 analyzes a form ofan argument of the circular arc interpolation command so as to determinewhether the circular arc interpolation command is a circular arcinterpolation command of a vector specifying type. Then, the commandargument determination unit 120 commands the circular arc shape formingunit 130 and the curved surface shape forming unit 140 to form a shape,based on the determination result.

In response to the command from the command argument determination unit120, the circular arc shape forming unit 130 performs circular arc shapeforming processing based on an argument specified by the circular arcinterpolation command so as to form a circular arc shape.

Further, in response to the command from the command argumentdetermination unit 120, the curved surface shape forming unit 140performs curved surface shape forming processing based on an argumentspecified by the curved surface interpolation command so as to form acurved surface shape. Here, the curved surface shape forming unit 140commands the circular arc shape forming unit 130 to form a circular arcshape which forms a part of a curved surface shape, when the curvedsurface shape forming unit 140 forms the curved surface shape.

The tool trajectory forming unit 150 forms a movement trajectory of atool based on the shapes formed by the circular arc shape forming unit130 and the curved surface shape forming unit 140.

Then, the distribution processing execution unit 160 performsinterpolation processing in which the tool trajectory formed by the tooltrajectory forming unit 150 is distributed into a movement amount forevery distribution cycle, so as to control respective servomotors 300,310, and 320.

FIG. 9 is a schematic flowchart of processing which is executed on thenumerical control apparatus 100 according to the present embodiment.Here, processing for forming a semicircular column shape is omitted inthis flowchart.

[Step SA01] A machining program is sequentially read and a command isanalyzed. When the analyzed command is a circular arc interpolationcommand (or a curved surface interpolation command), the process goes tostep SA02. When the analyzed command is not a circular arc interpolationcommand (or a curved surface interpolation command), the process goes toprocessing of other commands.

[Step SA02] An argument of the circular arc interpolation command whichis analyzed in step SA01 is determined so as to determine whether thecommand is a conventional argument specification in which a start point,an end point, a radius, and the like are specified. When the command isthe conventional argument specification, the process goes to step SA03.When the command is not the conventional argument specification, theprocess goes to step SA06.

[Step SA03] A circular arc shape which is specified by the conventionalargument specification is calculated.

[Step SA04] A tool trajectory is calculated based on the circular arcshape which is calculated in step SA03 or step SA09.

[Step SA05] A machine tool is controlled based on the tool trajectorywhich is calculated in step SA04 so as to perform a machining operationof the circular arc shape.

[Step SA06] Whether the command analyzed in step SA01 is a curvedsurface shape command or not is determined. When the command is thecurved surface shape command, the process goes to step SA10. When thecommand is not the curved surface shape command, the process goes tostep SA07.

[Step SA07] A coordinate (Xvs,Yvs,Zvs) of a vector origin is calculatedbased on the argument of the circular arc interpolation command.

[Step SA08] A coordinate of a point on the circular arc with which aleading end of the vector is brought into contact is calculated based onthe argument of the circular arc interpolation command and thecoordinate of the vector origin obtained in step SA07.

[Step SA09] The circular arc shape is calculated based on the startpoint, the end point, and the coordinate value, which is obtained instep SA08, of the point on the circular arc.

[Step SA10] A point (Xve,Yve, Zve) on a spherical surface is calculatedbased on an argument of a spherical surface shape command.

[Step SA11] A plane orthogonal to a direction, which is specified by theargument of the spherical surface shape command, of a vector iscalculated.

[Step SA12] A base circle is obtained based on the argument of thespherical surface shape command.

[Step SA13] An intersection point P of a straight line orthogonal to astraight line, which is obtained by connecting a start point and an endpoint, and the base circle is obtained.

[Step SA14] An equation of a sphere which passes through four pointswhich are the start point and the end point of the circular arc, thepoint (Xve, Yve, Zve) on the spherical surface, and the point P isobtained.

[Step SA15] A tool trajectory is calculated based on a curved surfacecircular arc shape which is obtained in step SA14 so as to performmachining of the curved surface shape based on the calculated tooltrajectory.

1. A numerical control. apparatus which enables specification of amovement trajectory of a circular arc shape by a circular arcinterpolation command which is included in a machining program,comprising: a program analysis unit which analyzes the machining programso as to acquire command data; a command argument determination unitwhich determines whether a vector is included in an argument of thecircular arc interpolation command which is included in the commanddata; a circular arc shape forming unit which forms a circular arc shapebased on the machining program, and a start point, an end point, and thevector, the start point, the end point, and the vector being specifiedby the argument of the circular arc interpolation command, when thecommand argument determination unit determines that the vector isincluded in the argument of the circular arc interpolation command; anda tool trajectory forming unit which forms a tool trajectory based onthe circular arc shape.
 2. The numerical control apparatus according toclaim 1, further comprising: a spherical surface shape forming unitwhich forms a spherical surface shape including a circular arc shapewhich is formed by the circular arc shape forming unit when the commandargument determination unit, the command argument determination unitdetermining whether the circular arc interpolation command is amachining command of a curved surface shape, determines that thecircular arc interpolation command is a machining command of a curvedsurface shape; wherein the tool trajectory forming unit forms a tooltrajectory based on the spherical surface shape.
 3. The numericalcontrol apparatus according to claim 2, wherein the spherical surfaceshape is a hemispherical surface shape including the circular arc shape,or a semi-circular column shape including the circular arc shape.